package session1;
import java.util.Iterator;
import java.lang.Iterable;

public class ResizingArrayStack<Item> implements Iterable<Item>
{
    private Item[] a = (Item[]) new Object[1];
    private int N = 0;
    public boolean isEmpty() {return N == 0;}
    public int size()        {return N;     }
    private void resize(int max)
    {
        Item[] temp = (Item[]) new Object[max];
        for (int i = 0; i < N; i++)
        {
            temp[i] = a[i];
        }
        a = temp;
    }

    public void push(Item item)
    {
        if(N == a.length) resize(2*a.length);
        a[N++] = item;
    }

    public Item pop()
    {
        Item item = a[--N];
        a[N] = null;
        if (N > 0 && N == a.length / 4) resize(a.length/2);
        return item;
    }

    public Iterator<Item> iterator()
    {
        return new ReverseArrayIterator();
    }

    private class ReverseArrayIterator implements Iterator<Item>
    {
        private int i = N;
        public boolean hasNext() {return i > 0;}
        public Item next() {return a[--i];}
        public void remove() {}
    }
}
